National Geographic News
Scientists in Texas have successfully cloned a cat, opening the way to replicating pets and other valued animals once the technique is perfected.
The kitten, called CC (the old typist's abbreviation for carbon copy) and now almost two months old, appears healthy and energetic, although she is completely unlike her tabby surrogate mother, Mark Westhusin and colleagues at Texas A&M University, College Station, announce in the February 21 issue of Nature.
The cat was cloned by transplanting DNA from Rainbow, a female three-colored (tortoiseshell or calico) cat into an egg cell whose nucleus had been removed, and then implanting this embryo into Allie, the surrogate mother.
"CC's coat color suggests that she is a clone, and a genetic match between CC and the donor mother confirms this," the researchers say.
She is not, however, identical to her DNA donor. The reason for this is that the pattern on cats' coats is only partly genetically determinedit also depends on other factors during development.
Out of 87 implanted cloned embryos, CC is the only one to survivecomparable to the success rate in sheep, mice, cows, goats, and pigs, the scientists say.
"If these odds can be shortened and CC remains in good health, pet cloning may one day be feasible," the scientists reported.
The technique used to clone the cat may not be readily extendable to other animals "if our understanding of their reproductive processes is limited or if there are species-specific obstacles," the scientists say.
In their first attempt, researchers obtained the cells used to make the clone from the skin cells of a "donor" cat. Eggs from other cats were used for the next step. Their chromosomes were removed and replaced with the DNA from the frozen cells, creating cloned embryos which were then transplanted into surrogate mothers.
"We carried out 188 such nuclear-transfer procedures, which resulted in 82 cloned embryos that were transferred into seven recipient females," the scientists said. Only one cat became pregnant, with a single embryo. But this pregnancy miscarried and the embryo was surgically removed after 44 days, when it was found to indeed be a cloned embryo.
In the next attempt the scientists tried using cells from ovarian tissue to receive the DNA from the cat to be cloned. Five cloned embryos made in this way were implanted into a single surrogate mother. Pregnancy was confirmed by ultrasound after 22 days and a kitten was delivered by C-section on December 22, 2001, 66 days after the embryo was transferred.
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